We get a hot ride in the prototype hybrid Porsche supercar: 94mpg, 70g/km and 800bhp...

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Top Gear has had a ride in the Porsche 918 Spyder. Not the concept car that arrived at the Geneva Motor Show in 2010 like lightning and earthquake. But the first test prototype of the production car. Now this really is what you'd call an early ride. The first customer doesn't get their car - in exchange for about £650,000 at today's exchange rate - until late 2013.

Given it's so early in development, you can forgive it looking like an absolute shed. The only vaguely production-shape panels are the doors. The rest is a mash-up of hack-sawed 911 panels and gaffer tape and naughty naked nudeness. The engineers don't even call it a prototype, but a ‘rolling chassis'.

Even so, now it's up and running, with the major systems on board, the engineers tell me they're confident of what this astounding car will do. Which is to meet or beat all the extravagantly purple performance claims their PR people invented for the show car.

We'll have the full story in the next issue of Top Gear Magazine. But here's the executive summary for all you time-poor internauts.

The performance headlines are this. Acceleration from 0-62mph in ‘less than three' seconds. Zero to 125mph in a time that almost matches a Bugatti Veyron. And a Nürburgring lap time (so far verified only on Porsche's supernaturally accurate simulators), of 7.22. That's 10 seconds faster than the old Carrera GT, and 10 seconds, to the sort of people who obsess on 'Ring times, is an entire geologic era.

But it's a hybrid. What Porsche calls, with admirable understatement, a ‘performance hybrid'.

Sure it can bumble along in electric mode for 15 miles, provided you charge the battery from the mains and then drive like you're on the way to court. And sure, in the very oddball conditions of the EU fuel cycle test, it emits just 70g/km of CO2 while doing 94mpg. But that isn't the point. When I ask if people would buy it to drive it like that, the engineers just smirk.

The point is when the V8 gets cracking. It's a 4.6-litre job that revs to 9000rpm and makes a crazed 570bhp. Where the concept car had its air intakes - just behind and above your head - the real car has its exhaust tips. It sounds beyond awesome. Even though in my ride they were rev-limiting it, the noise was bouncing around my cranium for hours after.

And then, on top of that, there are the front and rear electric motors. In the ‘race hybrid mode' their power is amped up so that between them these electric motors make 270bhp, which is more than the flat-six of an original 911 Turbo.

I can't begin to imagine the complexity of integrating these two motors with the V8 and a PDK gearbox, and getting it all to work smoothly in concert. But the engineers say there are 55 electronic controllers around the car. All I know is, to get into the passenger seat, I'm slipping my feet past enough cables to hold up a stadium roof.

We start off in electric-only mode and as promised the acceleration is smooth and swift. We get to about 60mph without a pause. The engineers say the final car will do an electric 0-62 in under 9.0 seconds, and go to 90mph-plus.

But the fun starts when we switch to the engine-plus-motors mode. That'll get you 800bhp in the production car, they now claim. The V8 cracks to life and the engineer slows right down before ragging it up through the seven-speed PDK transmission. When he lifts, I get some sense of what 0.5g of regenerative braking feels like (a figure AFAIK no other car has ever had).

We career up a test-track runway, and then peel off at 90 degrees down a second, wide straight, where the driver decides to demonstrate the steering fidelity. He saws at the wheel, I'm crunched by my harnesses, and breakfast nearly comes back to decorate his wiring loom. This is an extremely wide car, and it's so low your backside is barely higher than the paint of the lane markings. It grips like mad and doesn't roll a bit. It feels agile and light, even though the weight is the one statistic that's gone the wrong way since the concept car. Still, it's been held at below 1700kg.

Some more spec titbits from the production car... Carbon tub and panels. Carbon ceramic brakes. Four-wheel steering for better handling and stability. Aero with four separate moving aerodynamic devices. And, because it's Porsche, options that include a track chassis and lighter magnesium wheels.

With typically literal German humour, the production run is limited to 918 units. When one of those cars gets its Stig lap, we'd advise you to stick by your telly.

Meantime, sate your 918 appetite by buying the next issue of Top Gear Magazine.